Friday, September 13, 2013

New paper finds sugarcane plantation is a net source of CO2 to the atmosphere

A new paper published in Agricultural and Forest Meteorology finds a sugarcane plantation in Brazil acts as a net source of CO2 to the atmosphere. The paper adds to several other peer-reviewed papers finding various agricultural and ocean sites act as net sources of CO2 rather than sinks.

Highlights

Net carbon balance was measured during two climatically contrasting years.

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The dependence of CO2 exchange from light and saturation deficits.

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Water use efficiency during the main growth phases of a sugarcane bioenergy system.

Abstract

Fluxes of CO2 were measured above a sugarcane plantation using the eddy-covariance method covering two growth cycles, representing the second and third re-growth (ratoons) harvested with stubble burning. The total net ecosystem exchange (NEE) in the first cycle (second ratoon, 393 days long) was −1964 ± 44 g C m−2; the gross ecosystem productivity (GEP) was 3612 ± 46 g C m−2 and the ecosystem respiration (RE) was 1648 ± 14 g C m−2. The NEE and GEP totals in the second cycle (third ratoon, 374 days long) decreased 51% and 25%, respectively and RE increased 7%. Accounting for the carbon emitted during biomass burning and the removal of stalks at harvest, net ecosystem carbon balance (NECB) totals were 102 ± 130 g C m−2and 403 ± 84 g C m−2 in each cycle respectively [positive values indicate a net source]. Thus the sugarcane agrosystem was approximately carbon neutral in the second ratoon. Yield in stalks fresh weight (SFW) attained the regional average (8.3 kg SFW m−2). Although it was a carbon source to the atmosphere, observed productivity (6.2 kg SFW m−2) of the third ratoon was 19% lower than the regional average due to the lower water availability observed during the initial 120 days of re-growth. However, the overall water use efficiency (WUE) achieved in the first cycle (4.3 g C kg−1 H2O) decreased only 5% in the second cycle.